The treatment of opiate abuse and dependence by substitution of the abused opiate with a safer, longer-acting opioid is often a successful pharmacotherapeutic intervention strategy. Heroin, a widely abused opiate, acts as an agonist for the muopioid receptor (MOR). Heroin is often abused using intravenous injection, often resulting in needle-sharing among addicts, which is often responsible for the spread of life-threatening infections such as hepatitis C and HIV/AIDS. Methadone has been used as a substitute MOR agonist. Methadone is orally active, and has sufficient duration of action to enable it to be given as a single daily dose. More recently, buprenorphine 1, 21-(cyclopropyl-7α-[(S)-1-hydroxy-1,2,2-trimethylpropyl]-6,14-endo-ethano-6,7,8,14-tetrahydro-oripavine, a MOR partial agonist, has been used as a pharmacotherapy (see, e.g., U.S. Pat. No. 4,935,428). As a partial MOR agonist, it has a lower ceiling to its MOR-mediated effects than a full MOR agonist (e.g., methadone). As a result, buprenorphine has a greater margin of safety than full MOR agonists. In addition, buprenorphine also has a long duration of action. Buprenorphine's enhanced safety, coupled with its extended duration, enables a relatively long dosing interval, typically every 24 hours, but this can be extended to every 72 hours or more.
Buprenorphine's favorable safety profile compared to methadone has allowed it to be prescribed by office-based physicians, which has substantially decreased the cost of treatment, and increased the number of addicts in pharmacotherapy treatment.
For the treatment of opiate abuse and dependence, buprenorphine is available as tablets formulated for sublingual administration, and is sold under the trademark Subutex®. The daily maintenance dose for Subutex® is in the range 4-16 mg. Subutex® is readily soluble in aqueous media, making it possible for addicts to misuse the formulation by dissolving the tablets in water, and then injecting the resulting solution. To counter this misuse, buprenorphine has been formulated as a mixture with the MOR antagonist naloxone in a 4:1 ratio (Suboxone®).
Sublingual administration of buprenorphine has several drawbacks, notably the need to avoid swallowing the tablet because of buprenorphine's low bioavailability (˜5%) when taken orally. In comparison, buprenorphine's bioavailability is approximately fifty percent when absorbed sublingually (see, e.g., Jasinski and Preston, Buprenorphine, Ed. A Cowan, J W Lewis, Wiley-L is, NY pp. 189-211).
Several buprenorphine ester derivatives are described by Stinchcomb et al. in Pharm. Res (1995), 12, 1526-1529. The physiochemical properties of the esters are described, and compared with those of buprenorphine hydrochloride and its free base. Stinchcomb et al. also describe transdermal absorption of these esters in Biol. Pharm. Bull. (1996), 19, 263-267 and Pharm. Res. (1996), 13, 1519-1523. Wang, Published U.S. Patent Application No. 2005/0075361, also describes some buprenorphine derivatives, which are apparently useful for pain relief when delivered intramuscularly or subcutaneously.